Step Action
1 As the File System prepares new subtable lists and FSG loads new cylinders, the scanning task continues to read until the statement is satisfied or terminated.
2 Each time the scanning task moves to the next cylinder, the previous cylinder is immediately freed and returned to the list of free slots.
3 If the scanning task encounters a disk read error, the statement is aborted and all data processed so far is rolled back.

Changing the Cylinder Read Defaults

When Teradata RDBMS is installed, Cylinder Read is enabled by default and Cylinder Slots/AMP is set to 10. The feature is disabled automatically if FSG memory is calculated to be below 36 MB per AMP.

You can manually disable or re-enable Cylinder Read and/or change the number of slots per AMP using:

• Teradata MultiTool

• xctl utility (UNIX)

• ctl utility (Windows 2000)

The Cylinder Read setting and the Number of Slots/AMP value are interdependent, as follows:

15 - 2 Teradata RDBMS Database Administration

Chapter 15: Tools for Managing Resources

Managing I/O with Cylinder Read

IF the Cylinder Read field is set to . THEN .
DEFAULT the value for Cylinder Slots/AMP is calculated automatically. If you set the slider to a value, the setting is ignored.
USER you can set the Cylinder Slots/AMP value yourself. However, based on FSG cache size, in rare cases FSG may have to change the number of slots per AMP. (NCR recommends that as a general rule, the default setting should provide the best performance.) For an explanation and instructions on how to check the current allocation after a reset, see "Viewing the Cylinder Slot Configuration" on page 15-6.

For detailed instructions on setting Cylinder Read parameters, see the chapters titled "ctl Utility" and "xctl Utility" in Teradata RDBMS Utilities. For an explanation of how to use Cylinder Read for best results, see Teradata RDBMS Performance Optimization.

Viewing the Cylinder Slot Configuration

During reset, FSG recalculates the size of FSG cache and determines whether there is enough memory to allocate the number of slots per AMP that you selected. If not, or if you did not select a number, it attempts to allocate the default. Otherwise, it allocates as many slots as it can. For example, only 2 slots can be configured when FSG cache is down to 36 MB per AMP.

Therefore, although it should not happen often, it is possible that after a reset the number of slots configured by FSG may be different from your selection. When you need to know, you can find the actual slot configuration using the Database Window and the procedure outlined below. (For complete details on all the operations you can run in the Database Window, see Teradata RDBMS Database Window.)

Step Action
1 Access the Database Window.
2 Click on the Supvr icon to open the Supervisor window.
3 To bring up the File System Utility Routines (FSU) display, in the Enter a command: window, type: start fsudriver
4 When the FSU display appears, in the Enter a command: window, type the field number of the CylSlotInfo field: 93

Step Action
5 The field displays the current state of Cylinder Read and the number of slots
configured per AMP. The display should be similar to the following:
******** Cylinder Read Status ********
Cylinder Read is on.
9 slots allocated.
Hit return to continue

Calculating FSG Cache Size Requirements

The FSG Cache Percent field controls the percentage of memory to be allocated to FSG cache. You can change the value in FSG Cache Percent using the xctl utility (on UNIX) or ctl utility (on Windows 2000). To determine size, see:

The following fields have been added to the RSS_Svpr table. You can use these fields to track Cylinder Read behavior if you enable ResUsage logging.

For details on Resource Usage, see "ResUsage Reports" on page D-11 and Teradata RDBMS Resource Usage Macros and Tables. For information on how to best apply Cylinder Read, see Teradata RDBMS Performance Optimization.

This Cylinder Read field . Reports the .
Svpr_FileFcrRequests total number of times a cylinder read was requested.
Svpr_FileFcrDeniedThresh number of times a cylinder read request was rejected because FSG determined that either: • The number of data blocks to be loaded was below the threshold • It was more efficient to read the data blocks individually